/*
 * Copyright 2002-2021 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet.mvc.method.annotation;

import org.springframework.core.GenericTypeResolver;
import org.springframework.core.MethodParameter;
import org.springframework.core.ParameterizedTypeReference;
import org.springframework.core.ResolvableType;
import org.springframework.core.io.InputStreamResource;
import org.springframework.core.io.Resource;
import org.springframework.core.io.support.ResourceRegion;
import org.springframework.core.log.LogFormatUtils;
import org.springframework.http.*;
import org.springframework.http.converter.GenericHttpMessageConverter;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.converter.HttpMessageNotWritableException;
import org.springframework.http.server.ServletServerHttpRequest;
import org.springframework.http.server.ServletServerHttpResponse;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.CollectionUtils;
import org.springframework.util.StringUtils;
import org.springframework.web.HttpMediaTypeNotAcceptableException;
import org.springframework.web.accept.ContentNegotiationManager;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.context.request.ServletWebRequest;
import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
import org.springframework.web.servlet.HandlerMapping;
import org.springframework.web.util.UrlPathHelper;

import javax.servlet.ServletRequest;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.lang.reflect.Type;
import java.util.*;

/**
 * Extends {@link AbstractMessageConverterMethodArgumentResolver} with the ability to handle method
 * return values by writing to the response with {@link HttpMessageConverter HttpMessageConverters}.
 *
 * @author Arjen Poutsma
 * @author Rossen Stoyanchev
 * @author Brian Clozel
 * @author Juergen Hoeller
 * @since 3.1
 */
public abstract class AbstractMessageConverterMethodProcessor extends AbstractMessageConverterMethodArgumentResolver implements HandlerMethodReturnValueHandler {

    /* Extensions associated with the built-in message converters */
    private static final Set<String> SAFE_EXTENSIONS = new HashSet<>(
            Arrays.asList("txt", "text", "yml", "properties", "csv", "json", "xml", "atom", "rss", "png", "jpe", "jpeg",
                    "jpg", "gif", "wbmp", "bmp"
            ));

    private static final Set<String> SAFE_MEDIA_BASE_TYPES = new HashSet<>(Arrays.asList("audio", "image", "video"));

    private static final List<MediaType> ALL_APPLICATION_MEDIA_TYPES = Arrays.asList(
            MediaType.ALL, new MediaType("application"));

    private static final Type RESOURCE_REGION_LIST_TYPE = new ParameterizedTypeReference<List<ResourceRegion>>() {}.getType();


    private final ContentNegotiationManager contentNegotiationManager;

    private final Set<String> safeExtensions = new HashSet<>();


    /**
     * Constructor with list of converters only.
     */
    protected AbstractMessageConverterMethodProcessor(List<HttpMessageConverter<?>> converters) {
        this(converters, null, null);
    }

    /**
     * Constructor with list of converters and ContentNegotiationManager.
     */
    protected AbstractMessageConverterMethodProcessor(List<HttpMessageConverter<?>> converters,
                                                      @Nullable ContentNegotiationManager contentNegotiationManager) {

        this(converters, contentNegotiationManager, null);
    }

    /**
     * Constructor with list of converters and ContentNegotiationManager as well
     * as request/response body advice instances.
     */
    protected AbstractMessageConverterMethodProcessor(List<HttpMessageConverter<?>> converters,
                                                      @Nullable ContentNegotiationManager manager,
                                                      @Nullable List<Object> requestResponseBodyAdvice) {

        super(converters, requestResponseBodyAdvice);

        this.contentNegotiationManager = (manager != null ? manager : new ContentNegotiationManager());
        this.safeExtensions.addAll(this.contentNegotiationManager.getAllFileExtensions());
        this.safeExtensions.addAll(SAFE_EXTENSIONS);
    }


    /**
     * Creates a new {@link HttpOutputMessage} from the given {@link NativeWebRequest}.
     *
     * @param webRequest the web request to create an output message from
     * @return the output message
     */
    protected ServletServerHttpResponse createOutputMessage(NativeWebRequest webRequest) {
        HttpServletResponse response = webRequest.getNativeResponse(HttpServletResponse.class);
        Assert.state(response != null, "No HttpServletResponse");
        return new ServletServerHttpResponse(response);
    }

    /**
     * Writes the given return value to the given web request. Delegates to
     * {@link #writeWithMessageConverters(Object, MethodParameter, ServletServerHttpRequest, ServletServerHttpResponse)}
     */
    protected <T> void writeWithMessageConverters(T value, MethodParameter returnType,
                                                  NativeWebRequest webRequest) throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {

        ServletServerHttpRequest inputMessage = createInputMessage(webRequest);
        ServletServerHttpResponse outputMessage = createOutputMessage(webRequest);
        writeWithMessageConverters(value, returnType, inputMessage, outputMessage);
    }

    /**
     * Writes the given return type to the given output message.
     *
     * @param value         the value to write to the output message
     * @param returnType    the type of the value
     * @param inputMessage  the input messages. Used to inspect the {@code Accept} header.
     * @param outputMessage the output message to write to
     * @throws IOException                         thrown in case of I/O errors
     * @throws HttpMediaTypeNotAcceptableException thrown when the conditions indicated
     *                                             by the {@code Accept} header on the request cannot be met by the message converters
     * @throws HttpMessageNotWritableException     thrown if a given message cannot
     *                                             be written by a converter, or if the content-type chosen by the server
     *                                             has no compatible converter.
     */
    @SuppressWarnings({"rawtypes", "unchecked"})
    protected <T> void writeWithMessageConverters(@Nullable T value, MethodParameter returnType,
                                                  ServletServerHttpRequest inputMessage,
                                                  ServletServerHttpResponse outputMessage) throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {

        Object body;
        Class<?> valueType;
        Type targetType;

        // 设置 body
        if (value instanceof CharSequence) {
            body = value.toString();
            valueType = String.class;
            targetType = String.class;
        } else {
            body = value;
            valueType = getReturnValueType(body, returnType);
            targetType = GenericTypeResolver.resolveType(getGenericType(returnType), returnType.getContainingClass());
        }

        // 是 Resource 类型
        if (isResourceType(value, returnType)) {
            // 设置响应头
            outputMessage.getHeaders()
                    .set(HttpHeaders.ACCEPT_RANGES, "bytes");
            if (value != null && inputMessage.getHeaders()
                    .getFirst(HttpHeaders.RANGE) != null && outputMessage.getServletResponse()
                    .getStatus() == 200) {
                Resource resource = (Resource) value;
                try {
                    List<HttpRange> httpRanges = inputMessage.getHeaders()
                            .getRange();
                    outputMessage.getServletResponse()
                            .setStatus(HttpStatus.PARTIAL_CONTENT.value());
                    // 读取 resource 设置 body
                    body = HttpRange.toResourceRegions(httpRanges, resource);
                    valueType = body.getClass();
                    targetType = RESOURCE_REGION_LIST_TYPE;
                } catch (IllegalArgumentException ex) {
                    outputMessage.getHeaders()
                            .set(HttpHeaders.CONTENT_RANGE, "bytes */" + resource.contentLength());
                    outputMessage.getServletResponse()
                            .setStatus(HttpStatus.REQUESTED_RANGE_NOT_SATISFIABLE.value());
                }
            }
        }

        MediaType selectedMediaType = null;
        MediaType contentType = outputMessage.getHeaders()
                .getContentType();
        boolean isContentTypePreset = contentType != null && contentType.isConcrete();
        // 响应体设置了 ContentType 就使用
        if (isContentTypePreset) {
            if (logger.isDebugEnabled()) {
                logger.debug("Found 'Content-Type:" + contentType + "' in response");
            }
            selectedMediaType = contentType;
        } else {
            // 否则就根据 请求头 Accept 获取
            HttpServletRequest request = inputMessage.getServletRequest();
            List<MediaType> acceptableTypes;
            try {
                /**
                 * 拿到 Accept 的值
                 * */
                acceptableTypes = getAcceptableMediaTypes(request);
            } catch (HttpMediaTypeNotAcceptableException ex) {
                int series = outputMessage.getServletResponse()
                        .getStatus() / 100;
                if (body == null || series == 4 || series == 5) {
                    if (logger.isDebugEnabled()) {
                        logger.debug("Ignoring error response content (if any). " + ex);
                    }
                    return;
                }
                throw ex;
            }
            List<MediaType> producibleTypes = getProducibleMediaTypes(request, valueType, targetType);

            if (body != null && producibleTypes.isEmpty()) {
                throw new HttpMessageNotWritableException("No converter found for return value of type: " + valueType);
            }
            List<MediaType> mediaTypesToUse = new ArrayList<>();
            for (MediaType requestedType : acceptableTypes) {
                for (MediaType producibleType : producibleTypes) {
                    if (requestedType.isCompatibleWith(producibleType)) {
                        mediaTypesToUse.add(getMostSpecificMediaType(requestedType, producibleType));
                    }
                }
            }
            if (mediaTypesToUse.isEmpty()) {
                if (body != null) {
                    throw new HttpMediaTypeNotAcceptableException(producibleTypes);
                }
                if (logger.isDebugEnabled()) {
                    logger.debug("No match for " + acceptableTypes + ", supported: " + producibleTypes);
                }
                return;
            }

            MediaType.sortBySpecificityAndQuality(mediaTypesToUse);

            for (MediaType mediaType : mediaTypesToUse) {
                if (mediaType.isConcrete()) {
                    selectedMediaType = mediaType;
                    break;
                } else if (mediaType.isPresentIn(ALL_APPLICATION_MEDIA_TYPES)) {
                    selectedMediaType = MediaType.APPLICATION_OCTET_STREAM;
                    break;
                }
            }

            if (logger.isDebugEnabled()) {
                logger.debug(
                        "Using '" + selectedMediaType + "', given " + acceptableTypes + " and supported " + producibleTypes);
            }
        }

        // 将返回值内容 写入 到 HttpResponse
        if (selectedMediaType != null) {
            selectedMediaType = selectedMediaType.removeQualityValue();
            // 遍历 HttpMessageConverter
            for (HttpMessageConverter<?> converter : this.messageConverters) {
                GenericHttpMessageConverter genericConverter = (converter instanceof GenericHttpMessageConverter ? (GenericHttpMessageConverter<?>) converter : null);
                // 可写
                if (genericConverter != null ? ((GenericHttpMessageConverter) converter).canWrite(
                        targetType, valueType, selectedMediaType) : converter.canWrite(valueType, selectedMediaType)) {
                    /**
                     * 回调 beforeBodyWrite。可以在这个环节修改最终输出到response的内容
                     * {@link RequestResponseBodyAdviceChain}
                     *
                     * 是在这个地方初始化的
                     *  {@link ExceptionHandlerExceptionResolver#getDefaultReturnValueHandlers()}
                     * */
                    body = getAdvice().beforeBodyWrite(body, returnType, selectedMediaType,
                            (Class<? extends HttpMessageConverter<?>>) converter.getClass(), inputMessage, outputMessage
                    );
                    if (body != null) {
                        Object theBody = body;
                        LogFormatUtils.traceDebug(
                                logger, traceOn -> "Writing [" + LogFormatUtils.formatValue(theBody, !traceOn) + "]");
                        addContentDispositionHeader(inputMessage, outputMessage);
                        // 将返回值内容写到 outputMessage 中
                        if (genericConverter != null) {
                            genericConverter.write(body, targetType, selectedMediaType, outputMessage);
                        } else {
                            ((HttpMessageConverter) converter).write(body, selectedMediaType, outputMessage);
                        }
                    } else {
                        if (logger.isDebugEnabled()) {
                            logger.debug("Nothing to write: null body");
                        }
                    }
                    return;
                }
            }
        }

        if (body != null) {
            Set<MediaType> producibleMediaTypes = (Set<MediaType>) inputMessage.getServletRequest()
                    .getAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);

            if (isContentTypePreset || !CollectionUtils.isEmpty(producibleMediaTypes)) {
                throw new HttpMessageNotWritableException(
                        "No converter for [" + valueType + "] with preset Content-Type '" + contentType + "'");
            }
            throw new HttpMediaTypeNotAcceptableException(getSupportedMediaTypes(body.getClass()));
        }
    }

    /**
     * Return the type of the value to be written to the response. Typically this is
     * a simple check via getClass on the value but if the value is null, then the
     * return type needs to be examined possibly including generic type determination
     * (e.g. {@code ResponseEntity<T>}).
     */
    protected Class<?> getReturnValueType(@Nullable Object value, MethodParameter returnType) {
        return (value != null ? value.getClass() : returnType.getParameterType());
    }

    /**
     * Return whether the returned value or the declared return type extends {@link Resource}.
     */
    protected boolean isResourceType(@Nullable Object value, MethodParameter returnType) {
        Class<?> clazz = getReturnValueType(value, returnType);
        return clazz != InputStreamResource.class && Resource.class.isAssignableFrom(clazz);
    }

    /**
     * Return the generic type of the {@code returnType} (or of the nested type
     * if it is an {@link HttpEntity}).
     */
    private Type getGenericType(MethodParameter returnType) {
        if (HttpEntity.class.isAssignableFrom(returnType.getParameterType())) {
            return ResolvableType.forType(returnType.getGenericParameterType())
                    .getGeneric()
                    .getType();
        } else {
            return returnType.getGenericParameterType();
        }
    }

    /**
     * Returns the media types that can be produced.
     *
     * @see #getProducibleMediaTypes(HttpServletRequest, Class, Type)
     */
    @SuppressWarnings("unused")
    protected List<MediaType> getProducibleMediaTypes(HttpServletRequest request, Class<?> valueClass) {
        return getProducibleMediaTypes(request, valueClass, null);
    }

    /**
     * Returns the media types that can be produced. The resulting media types are:
     * <ul>
     * <li>The producible media types specified in the request mappings, or
     * <li>Media types of configured converters that can write the specific return value, or
     * <li>{@link MediaType#ALL}
     * </ul>
     *
     * @since 4.2
     */
    @SuppressWarnings("unchecked")
    protected List<MediaType> getProducibleMediaTypes(HttpServletRequest request, Class<?> valueClass,
                                                      @Nullable Type targetType) {

        Set<MediaType> mediaTypes = (Set<MediaType>) request.getAttribute(
                HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);
        if (!CollectionUtils.isEmpty(mediaTypes)) {
            return new ArrayList<>(mediaTypes);
        }
        List<MediaType> result = new ArrayList<>();
        for (HttpMessageConverter<?> converter : this.messageConverters) {
            if (converter instanceof GenericHttpMessageConverter && targetType != null) {
                if (((GenericHttpMessageConverter<?>) converter).canWrite(targetType, valueClass, null)) {
                    result.addAll(converter.getSupportedMediaTypes(valueClass));
                }
            } else if (converter.canWrite(valueClass, null)) {
                result.addAll(converter.getSupportedMediaTypes(valueClass));
            }
        }
        return (result.isEmpty() ? Collections.singletonList(MediaType.ALL) : result);
    }

    private List<MediaType> getAcceptableMediaTypes(
            HttpServletRequest request) throws HttpMediaTypeNotAcceptableException {

        return this.contentNegotiationManager.resolveMediaTypes(new ServletWebRequest(request));
    }

    /**
     * Return the more specific of the acceptable and the producible media types
     * with the q-value of the former.
     */
    private MediaType getMostSpecificMediaType(MediaType acceptType, MediaType produceType) {
        MediaType produceTypeToUse = produceType.copyQualityValue(acceptType);
        return (MediaType.SPECIFICITY_COMPARATOR.compare(
                acceptType, produceTypeToUse) <= 0 ? acceptType : produceTypeToUse);
    }

    /**
     * Check if the path has a file extension and whether the extension is either
     * on the list of {@link #SAFE_EXTENSIONS safe extensions} or explicitly
     * {@link ContentNegotiationManager#getAllFileExtensions() registered}.
     * If not, and the status is in the 2xx range, a 'Content-Disposition'
     * header with a safe attachment file name ("f.txt") is added to prevent
     * RFD exploits.
     */
    private void addContentDispositionHeader(ServletServerHttpRequest request, ServletServerHttpResponse response) {
        HttpHeaders headers = response.getHeaders();
        if (headers.containsKey(HttpHeaders.CONTENT_DISPOSITION)) {
            return;
        }

        try {
            int status = response.getServletResponse()
                    .getStatus();
            if (status < 200 || (status > 299 && status < 400)) {
                return;
            }
        } catch (Throwable ex) {
            // ignore
        }

        HttpServletRequest servletRequest = request.getServletRequest();
        String requestUri = UrlPathHelper.rawPathInstance.getOriginatingRequestUri(servletRequest);

        int index = requestUri.lastIndexOf('/') + 1;
        String filename = requestUri.substring(index);
        String pathParams = "";

        index = filename.indexOf(';');
        if (index != -1) {
            pathParams = filename.substring(index);
            filename = filename.substring(0, index);
        }

        filename = UrlPathHelper.defaultInstance.decodeRequestString(servletRequest, filename);
        String ext = StringUtils.getFilenameExtension(filename);

        pathParams = UrlPathHelper.defaultInstance.decodeRequestString(servletRequest, pathParams);
        String extInPathParams = StringUtils.getFilenameExtension(pathParams);

        if (!safeExtension(servletRequest, ext) || !safeExtension(servletRequest, extInPathParams)) {
            headers.add(HttpHeaders.CONTENT_DISPOSITION, "inline;filename=f.txt");
        }
    }

    @SuppressWarnings("unchecked")
    private boolean safeExtension(HttpServletRequest request, @Nullable String extension) {
        if (!StringUtils.hasText(extension)) {
            return true;
        }
        extension = extension.toLowerCase(Locale.ENGLISH);
        if (this.safeExtensions.contains(extension)) {
            return true;
        }
        String pattern = (String) request.getAttribute(HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE);
        if (pattern != null && pattern.endsWith("." + extension)) {
            return true;
        }
        if (extension.equals("html")) {
            String name = HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE;
            Set<MediaType> mediaTypes = (Set<MediaType>) request.getAttribute(name);
            if (!CollectionUtils.isEmpty(mediaTypes) && mediaTypes.contains(MediaType.TEXT_HTML)) {
                return true;
            }
        }
        MediaType mediaType = resolveMediaType(request, extension);
        return (mediaType != null && (safeMediaType(mediaType)));
    }

    @Nullable
    private MediaType resolveMediaType(ServletRequest request, String extension) {
        MediaType result = null;
        String rawMimeType = request.getServletContext()
                .getMimeType("file." + extension);
        if (StringUtils.hasText(rawMimeType)) {
            result = MediaType.parseMediaType(rawMimeType);
        }
        if (result == null || MediaType.APPLICATION_OCTET_STREAM.equals(result)) {
            result = MediaTypeFactory.getMediaType("file." + extension)
                    .orElse(null);
        }
        return result;
    }

    private boolean safeMediaType(MediaType mediaType) {
        return (SAFE_MEDIA_BASE_TYPES.contains(mediaType.getType()) || mediaType.getSubtype()
                .endsWith("+xml"));
    }

}
